1. Field of the Invention
The present invention relates generally to hard copy sheet processing apparatus. More specifically, it is concerned with mechanisms for separating successive sheets of stacked print media before they are fed into a sheet processing device.
2. Description of Related Art
Automated business machines for producing or reproducing hard copy documents (such as inkjet printers, electrophotographic printers, impact printers, copiers, facsimile machines, document scanners and the like) usually include (or are otherwise associated with) an automatic sheet feeder mechanism. Such mechanisms automatically unload successive single sheets from a stack of said sheets and then direct them to a workstation where a printing, copying, scanning, etc. apparatus carries out its intended function upon them.
Unfortunately, individual sheets in a stack of print media (such as a stack of paper) sometimes adhere to one another. This adherence has several causes: electrostatic charge between abutting sheets, sheet-to-sheet surface friction, chemical reactions between abutting sheets and/or the presence of edge debris on a stack of sheets. Regardless of the reason for it, when two or more sheets of print media adhere to one another, they constitute a misfeed into a sheet processing device.
Many sheet feeding mechanisms, and especially paper feeding mechanisms, operate by developing a frictional force between a sheet pickup device (such as a pad or roller) and the uppermost sheet in a stack of said sheets. The pad or roller is usually in physical contact with the top side of the top sheet in the stack. A frictional force between the pickup device and the top sheet causes the top sheet to be pulled off the stack and out of its holding tray when the sheet pickup pad or roller is moved forward in a linear movement and/or when a roller type pickup device is rotated while it is in contact with the top sheet. A stack of sheets from which successive top sheets are withdrawn also is usually held in pressure contact with the pickup device by the action of an upwardly directed biasing device such as a spring. Such a device urges a tray upon which the stack rests in an upward direction toward the paper pickup device. Thus, when the tray becomes empty, its bottom will come into direct contact with the paper pickup device. This circumstance can be used to generate a signal to reload the tray with a new stack of sheet stock. To this end, the tray is then moved downward against the upwardly directed force of the spring and reloaded.
Certain operational problems are associated with machines that include such automatic sheet feeders. The two most common problems are xe2x80x9cpaper jams,xe2x80x9d and xe2x80x9cmultiple sheet feedsxe2x80x9d. Paper jams interrupt sheet feed operations and require manual correction of the jam before automated conveyance of the paper can be restarted. That is to say that when a paper jam occurs, operation of the printer, copier, scanner, etc. must go into a standstill mode while waiting for a human operator to correct the problem. In this standstill mode, the operator has to first confirm the location of the paper jam and then remove the jam, usually by removing a sheet of paper lodged somewhere in the machine""s paper transport path.
Multiple sheet feed problems occur when two or more sheets of print media such as paper adhere to one another. Such adhering sheets often cause jams. Jams caused by multiple sheet feeds have the same undesirable consequences as jams having other causes. They also require the same kinds of manual clearing operations. Multiple sheet misfeeds also create pagination errors whereby adhering pages are not included in a sequenced array of pages because they were not sequentially printed, copied, scanned, etc. in an expected manner.
The present invention provides a sheet separating mechanism that serves to minimize the previously described multiple sheet feed problems and, hence, the jamming and improper pagination problems associated with them. The sheets being processed by applicant""s sheet separating mechanism will usually be print media such as paper. Those skilled in this art will, however, appreciate that other flexible (i.e., capable of being buckled or humped in a manner hereinafter described), sheet-like, materials can be separated just as well by the mechanisms described in this patent disclosure. Some of the more important components of applicant""s sheet separating mechanisms comprise: (1) a tray for containing a stack of sheets such as sheets of paper, (2) a sheet pickup arm having a sheet contact device for driving a top sheet of the stack in a forward direction, (3) a stopper wall capable of being placed in a substantially vertical orientation (to oppose forward movement of a top sheet) and in a substantially horizontal orientation (to allow forward movement of a top sheet) and (4) first and second sheet elevation stopper bars for defining the size and location of a hump in a top sheet by virtue of it being driven forward by the sheet contact device while being opposed by the stopper wall while it is in its vertical orientation.
Optionally, the sheet separating mechanism of this patent disclosure may further comprise a sheet takeup device into which the top sheet is fed when the stopper wall is lowered to its substantially horizontal orientation. In some still more preferred embodiments of this invention, applicant""s sheet separating mechanism will further comprise a sheet pickup arm that is equipped with a device having a configuration which is such that it is capable of powered rotation while in contact with the top surface of a top sheet. Pickup devices have round, elliptical, triangular and starwheel configurations that can perform this function. Pickup devices having round configurations are somewhat preferred. Hence, they will be used as the primary example in the specifications and drawings of this patent disclosure. In any case, powered rotation of such a pickup device can also serves to drive the top sheet forward. This powered rotation of a pickup device can be actuated before, during or after the forward driving action produced on the top sheet by a linear forward movement of the sheet pickup arm.
Other preferred embodiments of applicant""s sheet separating mechanism will include a sheet stack hold down device. Such a sheet stack hold down device is capable of upward and upward motion with respect to a given sheet in a stack as that sheet becomes the xe2x80x9ctopxe2x80x9d sheet in the stack. Preferably, the hold down device is lifted upward and out of contact with a top sheet just before said top sheet is driven forward by the forward movement of the sheet pickup arm. The hold down device is then lowered into contact with the next highest sheet in the stack so that it is not moved forward along with the top sheet. Still another preferred embodiment of this sheet separation mechanism will include a powered lift tray that automatically raises a stack as successive top sheets are removed from it.
The present invention serves to prevent, or at least thwart, multi-sheet misfeeds. It does this by imparting a sheet buckling or humping action to a forwardly moving top sheetxe2x80x94and to an underlying sheet that is adhering to the bottom surface of the top sheetxe2x80x94and to a sheet adhering to the bottom of the underlying sheet, and so on. Again, this forward motion can be imparted to the top sheet by virtue of it being in contact with a friction-creating pickup device (e.g., a pad, foot, roller, etc.) that is attached to a pickup arm that is capable of moving in a forward direction and then returning to its starting position at the appropriate time in the overall operation of this mechanism. Thus, as the pickup arm moves forward, it moves the top sheet forward as well. And as was previously noted, this forward movement of the top sheet can be augmented by (indeed, even entirely replaced by) powered rotation of a round, elliptical, triangular, starwheel, pickup device that is placed in physical contact with successive top sheets to be moved forward. Thus, a forwardly moving top sheet (and any underlying sheet(s) adhering to it) collide(s) with a vertical wall and, as a result thereof, is humped upward in its (their) center region(s). The hump is created between two bars that serve to define the location, contour and physical limits of the hump. that is capable of moving in a forward direction and then returning to its starting position at the appropriate time in the overall operation of this mechanism. Thus, as the pickup arm moves forward, it moves the top sheet forward as well. And as was previously noted, this forward movement of the top sheet can be augmented by (indeed, even entirely replaced by) powered rotation of a round, elliptical, triangular, starwheel, pickup device that is placed in physical contact with successive top sheets to be moved forward. Thus, a forwardly moving top sheet (and any underlying sheet(s) adhering to it) collide(s) with a vertical wall and, as a result thereof, is humped upward in its (their) center region(s). The hump is created between two bars that serve to define the location, contour and physical limits of the hump.